The present invention relates to electromagnetic transducers for information storage and retrieval systems, such as disk or tape drives.
Current commercially available disk drives employ magnetoresistive (MR) sensors for reading data, and store data in domains having magnetizations that are substantially parallel to concentric media tracks, the parallel magnetic storage sometimes called longitudinal recording. It has been predicted that such longitudinal magnetic storage will become unstable at normal operating conditions when the domains reach a minimal size, termed the superparamagnetic limit. In order to store the data at higher density, the drive system may instead be designed to store data in domains that are substantially perpendicular to the disk surface, which may be termed perpendicular recording.
FIG. 9 shows a prior art system for perpendicular recording, which includes an inductive transducer 20 positioned in close proximity to a surface 25 of a medium such as a disk 22. The inductive transducer 20 has a U-shaped core 30 formed of high-permeability, low-coercivity or “soft magnetic” material and the disk 22 has a soft magnetic underlayer 33, the core and underlayer forming a magnetic circuit indicated by flux lines 28 that traverse a higher coercivity media layer 32, for magnetizing the media layer or reading the magnetization of the media layer. The core has magnetic pole tips 36 and 38 that differ in media-facing area so that the magnetic signal is concentrated in the smaller pole tip for reading or writing data. The local portion of the disk may be traveling in the direction of arrow 40 or in a reverse direction, to write magnetic signals on a track. The pole tips are sufficiently separated to encourage magnetic flux to travel through the media, instead of across a submicron nonmagnetic gap that is typically employed for longitudinal recording. The prior art transducer of FIG. 9 is sometimes called a probe head.
U.S. Pat. No. 6,320,725 to Payne et al. discloses a transducer with a ring-shaped core terminating in a pair of pole tips that are separated by a nonmagnetic gap, with write fields emanating from corners of the pole tips closest to the gap, which may be termed a ring head. The ring head of Payne et al. has a head to medium spacing that is a fraction of the gap spacing, so that perpendicular rather than longitudinal write fields predominate in the media layer, with the leading corner of the trailing pole tip leaving the magnetic signal on the disk.
U.S. Pat. No. Re. 33,949 to Mallary et al. discloses a head for perpendicular recording with a write pole that is shielded with a downstream shield so that non-perpendicular fringe fields do not demagnetize the perpendicular signal written by the write pole. Mallary et al. note that reducing the spacing between the head and the medium allows the spacing between the write pole and the shield to be increased, because there is a greater incentive for flux to pass between the more closely spaced head and medium.